1. Field of the Invention
The present invention relates to crystal growth, and, more particularly, to growth of crystalline ceramic superconductors such as YBa.sub.2 Cu.sub.3 O.sub.7-.delta..
2. Description of the Related Art
High critical temperature ceramic superconductors were first announced in late 1986 by Bednorz and Muller, 64 Z.Phys. B 189 (1986) for a La-Ba-Cu-O system and early 1987 by Wu et al, 58 Phys.Rev.Lett 908 (1987) for a Y-Ba-Cu-O system. These discoveries unleased a flood of research on Cu-O based oxygen-deficient perovskite compounds aimed at practical superconducting applications. But the brittleness and instability with respect to processing variables of these compounds has limited use of standard fabrication techniques and led to searches for substitutes. For example, S.Jin et al, 51 Appl.Phys.Lett. 943 (1987) describes a method for drawing molten YBa.sub.2 Cu.sub.3 O.sub.7-.delta. into a wire; and M.Damento et al, 51 Appl.Phys.Lett 690 (1987) describes a method of crystal growth for YBa.sub.2 Cu.sub.3 O.sub.7-.delta. using an excess of CuO.
However, the known crystal growth methods can only produce relatively small crystals (3 mm by 3 mm by 0.2 mm) of YBa.sub.2 Cu.sub.3 O.sub.7-.delta. type compounds, and these crystals are usually embedded in the solidified melt from which they are grown and are difficult to remove. See for example, D.Kaiser et al, Growth of YBa.sub.2 Cu.sub.3 O.sub.z Single Crystals, 51 Appl.Phys.Lett. 1040 (1987). Further, the melt reacts with all crucible materials used, and this reaction (or wetting) dopes the melt and any crystals grown from it. See for example, M.Gurvitch et al, Preparation and Substrate Reactions of Superconducting Y-Ba-Cu-O Films, 51 Appl.Phys.Lett. 1027 (1987).